This invention relates generally to pumping apparatus particularly of the type commonly referred to as a mud pump for circulating drilling fluid in conjunction with deep well drilling processes, such as the drilling or reworking of oil wells, gas wells, water wells, and the like. More particularly, this invention relates to an improved so-called mud pump having multiple hydraulically driven piston assemblies adapted for delivering drilling fluid to a well at different substantially uniform pressures and flow rates while continuously cycling drilling fluid throughout all pump cylinders during all conditions of operation to prevent settling of particulate or solidification of the drillig fluid within any portion of the pump.
In the well drilling industry, such as original drilling, reaming, or reworking of oil and gas wells, water wells, and the like, a drilling tool is descended into the well and rotatably driven for drilling through earth and rock to appropriately increase the depth or diameter of the well bore. During such drilling processes it is necessary to circulate a drilling fluid into the well typically by flow downwardly through the drilling tool to lubricate the drilling process and to lift particulates soil and rock upwardly from the well through the annular space about the drilling tool. This drilling fluid, which commonly comprises a mixture of water, clays, and chemicals, is normally conveyed to a tank or pit at the surface where the particulate is allowed to settle prior to recirculation of the fluid into the well.
In the past, drilling fluid circulation pumps, commonly referred to as mud pumps, have conventionally comprised crankshaft-driven pumps having reciprocating pistons within cylinders to draw in drilling fluid upon piston retraction followed by piston extension to discharge the flow under pressure through a flow conduit to the well. However, in such pumps, the pistons typically move through relatively short strokes whereby relatively rapid crank shaft rotational speeds are required to develop the substantial fluid pressures required, typically on the order of several thousand psi. Moreover, such crankshaft-driven pumps inherently move the pistons with nonuniform velocities varying widely in accordance with the rotational position of the crankshaft. This velocity variation of the pistons results in nonuniform drilling fluid discharge which can create pulsations in fluid flow lines resulting in damage thereto. Still further, the many moving parts inherently required in crankshaft-driven pumps renders these pumps particularly susceptible to mechanical failures which, in the past, has been avoided only by constructing the pumps from extremely rugged, costly components.
Hydraulically driven piston pumps have been proposed for use in drilling fluid applications. See, for example, U.S. Pat. Nos. 2,169,703 and 3,650,638. While these hydraulically driven drilling fluid pumps overcome some of the nonuniform fluid delivery characteristics of crankshaft-driven piston pumps, hydraulically driven pumps have not been well accepted by the drilling industry. This lack of acceptance is due in part to the relative complexity and cost of previous hydraulic pumps, or alternatively, the inability of such pumps to delivery drilling fluid at different pressures and flow rates which are sometimes required without settling and/or solidification of drilling fluid within portions of the pump.
The present invention overcomes the problems and disadvantages encountered in the art by providing an improved hydraulically driven mud pump particularly designated for delivering drilling fluid at different selected flow rates and pressures wherein the pump is relatively simple in design and operation and further wherein drilling fluid is continuously circulated through all portions of the pump during all modes of operation.